Studies on intertrial priming have shown that in visual search experiments, the preceding trial automatically affects search performance: facilitating it when the target features repeat, and giving rise to switch costs when they change. These effects also occur at longer time scales: when one of two possible target colors is more frequent during an experiment block, this results in a prolonged and persistent facilitation for the color that was biased, long after the frequency bias is gone. In this study, we explore the robustness of such long-term priming. In one experiment, long-term priming was built up in one experimental session, and was then assessed in a second session a week later. Long-term priming persisted across this week, emphasizing that long-term priming is truly a phenomenon of long-term memory. In another experiment, participants were fully informed of the bias and instructed to prioritize the other, unbiased color. Nevertheless, long-term priming of the biased color persisted in this block. The results support the view that priming results from the automatic and implicit retrieval of memory traces of past trials.